Visual object recognition is central to our behavior, and knowledge of the underlying brain mechanisms is critical to understanding human visual perception and memory. The key problem is creation of selectivity for object identity that tolerates changes in an object's retinal image, such as changes in position and size. The primate brain appears to construct this selectivity in the ventral visual stream because neuronal responses in the highest area of that stream--the anterior inferotemporal cortex (AIT)--show shape selectivity that can tolerate position and size changes. Yet, we do not understand these key neuronal properties--reports of AIT tolerance are limited and inconsistent, and recent studies show that it can be very restricted. Thus, the goals of this proposal are an understanding of key factors likely to determine AIT position and size tolerance, and to determine if AIT tolerance can explain behavioral tolerance. Our first aim is to systematically determine the position and size tolerance of AIT neuronal shape selectivity for a range of object sets and object training histories. We will establish the relationship of selectivity and AIT position and size tolerance, the interaction of AIT position and size tolerance, and the effect of object-specific training on these relationships. These data will establish neuronal tolerance at the highest level of the primate visual system and provide a much-needed foundation for further study. The mechanisms that might underlie position and size tolerance fall into two broad classes: (1) automatic generalization;and (2) tolerance learned by experiencing objects across changes in position and size. Our second aim is to determine if position- or size-specific object experience have substantial effects on the position or size tolerance of AIT shape selectivity. Because this has not been examined, any result would be extremely informative in constraining mechanisms and guiding future studies. Although it is thought that AIT tolerance underlies behavioral tolerance, this has not been systematically examined. Our third aim is to determine if the position and size tolerance of object identification can be explained by the tolerance of AIT neuronal shape selectivity. This is a vital to understanding the link between high-level, ventral stream neuronal responses and visual object identification.